Skyrmions are topologically protected field configurations with
particle-like properties which were believed to crystallize only
under non-equilibrium conditions. Recently, it has been predicted
that they can also become ground states in magnetic systems with
broken inversion symmetry [1]. We give theoretical evidence of a
two-dimensional lattice of atomic-scale skyrmions as the magnetic
ground state of a monolayer Fe on Ir(111), a system which has
been studied by spin-polarized scanning tunneling microscopy [2].
We apply an extended Heisenberg model based on parameters
determined from first-principles to identify the four-spin
interaction as its microscopic origin. This interaction couples
degenerate spin spirals and enforces a square-symmetry on the
skyrmionic spin texture decoupled from the underlying hexagonal
atomic lattice. [1] U. K. R\"o{\ss}ler et al., Nature 442, 797
(2006).
[2] K. von Bergmann et al., PRL 96, 167203 (2006).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2010.MAR.L34.14